Traditionally, used paper and agricultural byproducts, such as sawdust, wood waste, corncobs, straw, sugar cane bagasse, rice hulls, and the like, have been regarded essentially as waste materials, and have been disposed of through incineration or by other, similarly unproductive means. It is well known that the cellulosic constituents of such materials can be hydrolyzed to produce more valuable products; however, such operations are in limited use, due largely to the relatively low return-on-investment which they are capable of generating. The capital expenditures required to design and construct the facilities necessary for carrying out such recovery operations tend to be very significant, thus demanding that relatively high conversion rates be attainable, in order to justify the expense involved. Moreover, the ready availability of the same or similar reaction products, from alternative sources and at relatively low cost, renders it that much more difficult to justify the adoption and use of any new scheme.
The presently known methods of hydrolyzing cellulosic materials are not, by-and-large, considered to be commercially feasable, for a number of reasons. In certain instances, the processes are not readily adapted to continuous operation; they typically require excessively long reaction times, and the reactions are normally carried out at low solids concentrations, all of which seriously limits productivity. Moreover, the known methods do not afford such control as would enable utilization to produce products of greatest value and salability.
A major impediment to the development of a commercially practical hydrolysis process resides in the reactor system employed. In a broad sense, the systems heretofore designed have not, so far as is known, permitted a sequence of operations to be carried out in such a manner as would permit the throughput rates and reaction control that are now deemed to be necessary to commercial feasibility. In a more specific sense, the focal point of the inadequacy of prior attempts to carry out hydrolysis, in the high solids concentrations required for adequate economics, lies in the inability to introduce efficiently the relatively dry mixtures which characterize a high solids cellulosic feed material. In other words, pumping apparatus presently available is not capable of reliably handling the feed materials which must be used to render a commercial method economically justifiable.
Accordingly, it is an object of the present invention to provide a novel reactor system for continuously effecting the hydrolysis of cellulosic materials as relatively concentrated aqueous mixtures.
It is also an object of the invention to provide such a system which is capable of handling mixtures of the foregoing type, which reduce the tendency for the mixtures to dewater, and thereby clog the system.
A more specific object of the invention is to provide high solids pump apparatus suitable for use in such a system, through which the high solids aqueous mixtures may move relatively freely, thereby minimizing dewatering and clogging, which apparatus is also capable of feeding the material at high rates and with good efficiency.
Even more specific objects are to provide a novel valve, so designed as to promote such operation of the pump apparatus, and a hopper arrangement which contributes significantly to the simplicity and efficiency of the system.
Yet another object of the invention is to provide such a system, apparatus and valve, which are of relatively uncomplicated construction, and of modest cost.